Determining the coke forming tendency of petroleum products frequently involves the use of the Conradson Carbon Residue test. The Conradson Carbon Residue (CCR) test is designed to indicate the extent of coke that a petroleum product will form under thermal degradation conditions, such as might be encountered in distillation towers, heat exchangers, and reactors. Since its inception, the CCR test has been applied to characterize a multitude of petroleum products and is currently defined by ASTM D 189-76 and IP 13/66.
Despite the popularity of this widely used standard, there are disadvantages to the CCR test. For example, the test is generally slow, lacks precision, and requires the utilization of large samples (5-10 grams). Due to the utilization of an open flame and the resultant smoke, the CCR test is also hazardous and messy.
In light of these shortcomings, work was undertaken by Fern Noel of Imperial Oil Ltd., Canada, to develop a procedure or method which would duplicate the results of the CCR test, but overcome the disadvantages thereof. The easier, more precise, and faster method developed by Fern Noel for obtaining the same results as the CCR test was set forth in an article entitled An Alternative To The Conradson Carbon Residue Test, the disclosure of which is incorporated by reference. The method and results described therein had initially been disclosed by Noel at a meeting of the American Chemical Society (ACS) in Las Vegas in August of 1980 and copies of Noel's presentation were made available at that time.
Under the standard CCR procedure, there is no purge of the system with an inert gas, such as nitrogen, at any time during the test. However, the results of Noel's experiments indicated that the presence of trace amounts of oxygen during the early stages of coking caused the formation of slightly more coke. Nevertheless, Noel's object was to produce results equivalent to CCR values regardless of this effect.
Noel determined that coke values similar to the CCR test values could be obtained using conditions and equipment other than that defined by the American Society of Testing Materials (ASTM). Noel's results prescribed the following conditions for optimum correlation with the CCR test:
1. Temperature of 500.degree. C..+-.10.degree. C. PA1 2. Coking time not less than 20 minutes. PA1 3. Nitrogen blanketing. PA1 4. Heating rates of (2.degree. to 40.degree. C./min) up to coking temperature of 500.degree. C. PA1 5. Sample container should be glass. PA1 6. Glass cups of 3.times.1 cm can be used for sample sizes of 30-100 mg. For smaller samples, sample cups should be decreased in size to avoid the thin film effect.
Using the basic groundwork of Noel's work, the assignee of the present invention began development of a single unit tester oven that would provide all the advantages of the new method. The development of the present invention was assisted by the coincidental market introduction of a programmable controller by the Barber-Colman Co., Model 570. Nevertheless, the invention oven may utilize any one of several possible heat control means and is designed to achieve any type of small scale batch heating of liquids or solids in an ambient pressure gas atmosphere.
The present invention achieves the advantages of Noel's new carbon residue testing method by providing an oven wherein a petroleum product may be heated in a preselected gas atmosphere. The oven comprises an inner heating chamber having a cylindrical wall with a plurality of purge gas inlet ports therethrough near a top opening thereof and a bottom floor having a gas outlet port therethrough. The gas outlet port permits the passage of purged oxygen and petroleum gas from the inner heating chamber into a gas exhaust tube during the purging phase and heating phase, respectively. The top opening of the inner heating chamber permits the introduction of the petroleum product into the heating chamber, the top of which has a chamfered edge for receiving thereon a spherical gravity lid. The inner heating chamber and gas exhaust tube are surrounded by an outer gas flow chamber and an ante chamber, respectively, the outer gas flow chamber being in communication with the ante chamber and having a plurality of concealed heater elements therein contiguous to the outer wall of the inner heating chamber. The heater elements are continuously monitored by a programmable external controller which is in communication with a thermocouple protruding through the inner wall of the inner heating chamber, thereby permitting the product within the sealed inner heating chamber to be heated evenly at the rate and temperature desired.
During the operation of the oven, a glass vial containing the liquid or solid product to be heated is introduced to the inner heating chamber and subsequently sealed therein by the gravity lid. A preselected inert or reactive purge gas is thereafter introduced to the ante chamber and flows therefrom into the outer gas flow chamber around the heater elements and into the inner heating chamber through the gas inlet ports. The lighter purge gas initially purges the inner heating chamber of oxygen by gradually urging the denser air through the gas outlet port into the gas exhaust tube. After the inner heating chamber has been sufficiently purged, the product is heated at the rate and temperature specified by the controller program. Throughout the heating phase, the lighter purge gas continues to purge the inner heating chamber of volatile vapor or gas by urging the denser vapor through the gas outlet port and gas exhaust tube. The cool purge gas entering the oven through the ante chamber cools the gas outlet port resulting in a cooler surface that causes much of the vapor within the gas exhaust tube to condense therein. The condensed product is thereafter collected in a condensate trap connected to the bottom of the oven at the termination of the gas exhaust tube. The oxygen and process or product vapor that does not condense is properly removed from the oven through an exhaust chimney which is connected to the gas exhaust tube and in communication with an exhaust hood.